Processes for patterning semiconductor wafers typically rely on lithographic transfer of a desired image from a thin-film of radiation-sensitive resist material. The process entails the formation of a sacrificial layer, the xe2x80x9cresistxe2x80x9d, which is photo-lithographically patterned. Generally these resists are referred to as xe2x80x9cphotoresistsxe2x80x9d.
The patterning of the resist involves several steps, including exposing the resist to a selected light source through a suitable mask to record a latent image of the mask and then developing and removing selected regions of the resist. For a xe2x80x9cpositivexe2x80x9d resist, the exposed regions are transformed to make such regions selectively removable; while for a xe2x80x9cnegativexe2x80x9d resist, the unexposed regions are more readily removable.
The pattern can be transferred into surface texture in the wafer by etching with a reactive gas using the remaining, patterned resist as a protective masking layer. Alternatively, when a wafer is xe2x80x9cmaskedxe2x80x9d by the resist pattern, it can be processed to form active electronic devices and circuits by deposition of conductive or semiconductive materials or by implantation of dopants.
Materials used in single layer photoresists for optical lithography should meet several objectives. Low optical density at the exposure wavelength and resistance to image transfer processes, such as plasma etching, are two important objectives to be met by such a photoresist material. Shorter wavelengths of radiation permit greater resolution. The most common wavelengths currently used in semiconductor lithography are 365 nm and 248 nm. The desire for narrower linewidths and greater resolution has sparked interest in photoresist materials that can be patterned by even shorter wavelengths of light.
All manufacturing of integrated circuits has been enabled by high-performance spin-on organic polymeric photoresists. If organic resists continue in their critical role within the ever shrinking resolution demands of advanced lithography, the stringent process window demands at sub-100 nm resolution will need to be met by resists possessing sufficient sensitivity to meet the equally demanding required throughput.
Resists should maintain critical linewidth control throughout the patterning process, including both imaging and subsequent transfer via plasma etch. Line-edge roughness on the order of 5 to 10 nm is a concern at 250 nm, but will render a lithographic process unworkable when critical dimensions fall to below 100 nm. Furthermore, transferring imaged patterns via plasma etch requires that a sufficient resist be present to act as an etch mask, but single layer resists appear to be limited by an aspect ratio of 3:1. As critical features approach 25 nm, resist thickness is expected to drop to under 100 nm, a thickness that does not allow plasma image transfer even with a several fold improvement in plasma etch selectivity.
Unless plasma etch selectivity increases several fold (an unlikely event with organic based resists) single layer resist chemistry will cease to be practical at sub-100 nm resolution. Multilayer resist schemes offer the capability of increased aspect ratio, but they add to the process complexity and cost. Therefore, a need exists to provide photoresists which meet these challenging demands.
This invention generally relates to photoresist materials useful in lithography and, particularly, to improved materials and methods for pattern formation on semiconductor wafers.
The present invention pertains to encapsulated inorganic resist technology (EIRT) and their methods of preparation which represents a fundamentally new type of resist concept, which is compatible with conventional resist processing. In resists of the invention, an inorganic core particle or colloidal particle is encapsulated under a photochemically active layer, which upon exposure can modify the particle""s solubility, leading to developer differentiation.
In one aspect of the invention, encapsulated inorganic resists represent a fundamentally new type of resist material, which is compatible with conventional resist processing such as spin casting from organic solvents and development with aqueous 2.38% TMAH developers. A key feature of the resist is the use of encapsulated inorganic materials as resist components, a fact that significantly increases the plasma etch selectivity of EIRT (encapsulated inorganic resist technology) resists compared to conventional polymeric resists. In effect, these resist systems act as a photoimagable single layer hard mask, although use as the top layer in a bilayer resist scheme is contemplated.
The present invention pertains to the surprising discovery that durable, high resolution photosensitive resist compositions, e.g. on the order of molecular pixel sizes of less than 10 nanometers (nm), can be prepared from the combination of a resin binder and an encapsulated inorganic material, e.g., a metallic oxide. The particle dispersions have solution characteristics and allow conventional resist processing. The photosensitive resist composition can be either a positive or negative photosensitive resist, depending upon the resin binder system chosen.
The encapsulated inorganic materials useful in the invention include metals, metal salts and metallic oxides. For example, metallic oxides useful in the invention are the oxides of silicon, aluminum and titanium. Typically the content of the encapsulated inorganic material is between about 0.1% and about 90% by weight of the photosensitive resist composition; preferably between about 5.0% and about 75% and most preferably between about 10% to about 50% by weight. In a most preferred embodiment, the binder and the encapsulated inorganic material form a clear photosensitive resist composition. This clear composition is transparent or translucent to the eye and can be considered a solution or a dispersion. It has been unexpectedly discovered that the combination of the encapsulated inorganic material and resin binder forms a clear solution without precipitation of the encapsulated inorganic material from solution. This unexpected advantage provides one of ordinary skill in the art with the ability to coat a substrate without having to take any additional steps to insure that the energy applied to the photosensitive film to cure the film without having inconsistencies within the photoresist film caused by suspended opaque solids.
Silicon containing particles, e.g., 1-5 nm diameter particles (commercially available as 8-10 nm particles) of this size offer two important advantages in resist design. First, the small molecular size allows for high resolution systems with a relatively small molecular pixel size of less than 5 nm. This can be compared to traditional organic polymer based resists, which have polymeric molecular weights between 5,000 and 20,000 Daltons and molecular pixel sizes of 4 to 9 nm. Critical dimension control and line edge roughness at sub-100-nm resolution is extremely sensitive to the fine details of the molecular structure including the molecular pixel size. Secondly, particle dispersions comprised of this small molecular size behave for all intents and purposes as a solution and allow conventional resist processing including spin casting from organic solvents and aqueous base, such as 2.38% TMAH development.
The photosensitive resist compositions of the invention can further include a surfactant and/or a solvent.
The photosensitive resist compositions of the invention are sensitive to conventional 455 nm (g-line), 405 nm (h-line), or 365 nm (i-line) steppers; at either 248 or 193 nm due to decreased resist absorbance; and/or sensitive to imaging sources such as 157 nm, EUV, e-beam, x-ray, ion beam, and other sub-200 nm wavelengths.
Other advantages of the invention will be readily apparent to one having ordinary skill in the art upon reading the following description.
All percentages by weight identified herein are based on the total weight of the photosensitive resist composition unless otherwise indicated.